Etching method and etching equipment

ABSTRACT

The invention provides an etching method for realizing trench etching without causing any damages to the side walls of the trench while maintaining a high-etching rate. The plasma etching method relates to forming a groove or a hole by forming a silicon trench to a silicon substrate or a silicon substrate having a silicon oxide dielectric layer via a mixed gas plasma containing a mixed gas of SF6 and O2 or a mixed gas of SF6, O2 and SiF4 and having added thereto a gas containing hydrogen within the range of 5 to 16% (percent concentration) of the total gas flow rate of the mixed gas.

The present application is based on and claims priority of Japanesepatent application No. 2005-295462 filed on Oct. 7, 2005, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and equipment for etching asemiconductor device. More specifically, the present invention relatesto a method and equipment capable of preventing the side walls of atrench (groove or hole) from being damaged.

2. Description of the Related Art

Recently, silicon (Si) trench etching is applied as a device isolationtechnique to devices such as in-vehicle pressure-resistant IGBT(insulated gate bipolar transistor) devices corresponding to hybridvehicles, which is drawing keen attentions in the motor vehicleindustry. This method relates to electrically isolating devices byforming a deep trench via dry etching to the device isolation region ofthe semiconductor device, and embedding an insulating film to the formedtrench via CVD (chemical vapor deposition) method or the like.

Moreover, there are active attempts to apply this Si trench to athree-dimensional mount technology, which also requires a deep trench tobe formed via etching as described above.

In forming the above-mentioned trench, the depth of the hole (or groove)of the trench profile is required to be as deep as several tens ofmicrometers, so in order to ensure sufficient throughput, the etchingmust be performed at high etching rate. Fluoride-based gases havinghigher reactivity with Si is dominant over chlorine-based gases in themethod for realizing high-rate plasma etching.

Japanese Patent Application Laid-Open Publication No. 11-135489 (patentdocument 1) discloses, for example, a dry etching method carried out byadding approximately 80 to 150 mL/min of HBr (hydrogen bromide) gas to amixed gas (total flow rate being 24 mL/min) consisting of SF6/O2/SiF4(sulfur hexafluoride/oxygen/silicon tetrafluoride) to enhance the ionetching performance and to control the trench angle profile to around 90degrees.

Japanese Patent Application Laid-Open Publication No. 2004-87738 (patentdocument 2) discloses a dry etching method for processing a trench via amixed gas plasma using a mixed gas consisting of SF6, O2 and SiF4 toprocess trenches with an opening diameter or opening width of 3micrometers or smaller and a depth of 15 micrometers or smaller, or anopening diameter or opening width of 3 micrometers or larger and a depthof 20 micrometers or deeper.

However, according to the above-mentioned prior art performing high-rateetching using mainly fluorine-based gases, the effect of protecting theside walls of the trench is insufficient, and especially when forming adeep trench, the protection of the upper portion of the side walls ofthe etched trench becomes insufficient while the etching is progressedin the depth direction, causing damages such as recess and roughness tobe generated on the surface of the side walls.

That is, considering the embedding process that follows the forming ofthe trench, the trench must be somewhat tapered, and in that case, thetapered portion of the trench is subjected to damage by the ionbombardment if the ionicity is high. However, there is no considerationon the above problem according to the prior art method disclosed inpatent document 1, and since the method carries out etching with highionicity, the ion bombardment on the inner wall surfaces of the trenchmay damage the protective layer and generate recesses and surfaceroughness on the side walls.

Further, according to the prior art method disclosed in patent document2, there is no disclosure on an etching method related to processing atrench with a small opening (under 3 micrometers) and a deep hole (over20 micrometers) with a high aspect ratio. Since the etching method for atrench having a high aspect ratio is not established according to patentdocument 2, the protections on the upper portion of the side walls ofthe trench having completed etching becomes insufficient, and the sidewalls are damaged at the end of the etching process.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an etching method andan etching apparatus capable of etching a trench without causing anydamages, such as recess and surface roughness, on the side wall surfaceof the trench while maintaining a high-etching rate.

The object of the present invention is realized by carrying out plasmaetching for forming a silicon trench to create a groove or a hole to asilicon substrate or a silicon substrate having a silicon oxidedielectric layer, the etching performed via a plasma generated by amixed gas containing hydrogen formed by adding a gas containing hydrogento a mixed gas composed of SF6 and O2 or a mixed gas composed of SF6, O2and SiF4, wherein the amount of added gas containing hydrogen is withina range of 5 to 16% (percent concentration) of the total gas flow rateof said mixed gas.

According to the present invention, a trench profile having no side walldamage can be formed while maintaining a high-etching rate, that is,while maintaining throughput. Furthermore, since the protection of theside walls of the trench is realized by adding gas containing a smallamount of H (hydrogen), the rapid increase of reaction byproductsattaching to the inner walls of the chamber can be disregarded, and theinside of the chamber can maintain a clean condition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a microwave plasma etching equipment according to thepresent invention;

FIG. 2(a), FIG. 2(b) and FIG. 2(c) illustrate a damage generated to thesurface of side walls of a Si substrate according to the prior art;

FIG. 3(a), FIG. 3(b) and FIG. 3(c) show dependencies of adding HBraccording to the present invention; and

FIG. 4(a) and FIG. 4(b) show etching profiles obtained by the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments for carrying out the present invention will bedescribed in detail with reference to the drawings.

Embodiment 1

FIG. 1 shows a microwave plasma etching equipment according toembodiment 1 of the present invention utilizing microwaves and magneticfields as means for generating plasma.

In the present equipment, etching gas is supplied to an etchingprocessing chamber 101 from a gas supply means 104 via a permeationwindow 105 having a porous structure made of quartz, for example.

Further, microwaves generated from a microwave generator (not shown) aretransmitted via a matching box 106 and a wave guide 107 and through amicrowave introduction window 108 into the etching processing chamber101 to turn the above-mentioned etching gas into plasma.

In order to enhance the radiation efficiency, a solenoid coil 109 forgenerating magnetic fields is disposed around the etching chamber, amagnetic field of 0.0875 T is generated, and high-density plasma isgenerated by the magnetic field utilizing electron cyclotron resonance.A sample stage 103 is disposed in the etching chamber 101, on which asubstrate to be processed 102 is placed, which is subjected to etchingby gas plasma generated via microwaves. A high-frequency power source113 is connected to the sample stage 103 for placing the object to beprocessed, which is designed to apply a high frequency bias in the rangeof 400 kHz to 13.56 MHz. A static adsorption force is generated on thesurface of the sample stage 103 by applying DC voltage through a staticadsorption power source 110, and the substrate 102 to be processed isattracted to the sample stage 103 via static chuck.

Further, grooves are formed on the surface of the sample stage 103, sothat by feeding cooling gas such as He, Ar and O2 from a cooling gasinlet 112 to a flow channel (not shown) defined by the grooves and theback surface of the substrate 102 to be processed fixed thereto, thechannel can be maintained at predetermined pressure. The rise oftemperature of the surface of the substrate 102 to be processed istransmitted via thermal conduction between the gas in the channel andthe contact surface to the surface of the sample stage 103, by which thesubstrate is maintained at a constant temperature. In order to cool thesubstrate 102 to be processed to 0 degrees or lower, a coolant having atemperature cooled to a predetermined temperature by a chiller unit 111is circulated in a coolant circulation channel embedded in the samplestage 103.

An insulating cover 114 made of ceramics or quartz is disposed aroundthe substrate 102 to be processed. The etching gas introduced into theetching chamber 101 is discharged to the exterior of the etching chamber101 after the etching is completed via an exhaust pump and exhaust pipenot shown.

Next, the actual embodiment of the Si etching method according to thepresent invention will be described.

In the present embodiment, an example of a process is illustrated byusing the above-described plasma etching equipment to carry out a plasmaprocess primarily using a mixed gas composed of SF6, O2 and SiF4. Thedetailed structure of the substrate 102 to be processed and the statusafter the etching is illustrated in FIG. 2.

As shown in FIG. 2(a), the substrate 202 to be processed is an Sisubstrate patterned by a mask material 201 consisting of SiO2 or thelike, and as shown in FIG. 2(b), the substrate is etched through atrench opening 203. In this etching process, the SF6 and O2 gasesintroduced to the etching chamber 101 are dissociated into ions andradicals of Si, S, F and O, respectively, and SiF and SiO are generatedby the reaction with the surface of the substrate 202. The SiF generatedduring this reaction process and the SiF generated by the dissociationof SiF4 gas lead the etching performed within the trench opening 203.

On the other hand, simultaneously with the progress of the etchingwithin the trench opening 203, an appropriate amount of SiO is formed asa side wall protecting film, by which the isotropic etching by Fradicals is suppressed and an anisotropic high-rate etching is enabled.Moreover, since the SiO generated by the reaction of mixed gas composedof SF6 and O2 gases with the silicon in the substrate is deposited as arelatively thin layer on the inner wall of the chamber, only very littlecontaminants are generated by detached attachments, so the wetting cycleof the chamber can be advantageously elongated.

Furthermore, according to the above explanation, it was necessary thatSiF4 was contained in the mixed gas. However, gases such as SF6 and O2can be used to achieve the objects of the present invention as long asan appropriate amount of SiO is deposited as a side wall protectionlayer.

As shown in FIG. 2(b), if the trench depth is relatively shallow (orwhen the etching time is short), the side walls of the trench are notdamaged, and the etching can be carried out by the present processwithout any problem. However, if the etching is carried out to a furtherdepth as shown in FIG. 2(c), the progress of the etching in the depthdirection causes the protection of the side walls to be insufficient,and as a result, a damaged side wall 204 is generated.

According to the present process, it is possible to to suppress suchdamage 204 to the Si surface by reducing the amount of fluorine radicalsacting as the etchant, but in that case, the etching in the depthdirection is also suppressed, according to which the etch rate isdeteriorated or the etching is stopped.

Thus, one example of a process according to the plasma etching method ofthe present invention will be described with reference to FIG. 3.

FIG. 3 illustrates the results of trench etching carried out by addingHBr (hydrogen bromide) to the aforementioned etching conditions. As anexample, by adding 30 mL/min of HBr to a mixed gas composed of 150mL/min of SF6, 30 mL/min of O2 and 200 mL/min of SiF4, the surfacedamage 204 generated to the Si trench was suppressed. In the example,the amount of HBr gas being added is approximately 8% (percentconcentration) of the total gas flow rate.

FIG. 3(a) illustrates the Si trench etching quantity dependency showingthe quantity of etched Si (m) with respect to the added flow rate of HBr(mL/min). When the added flow rate of HBr is relatively small (0 to 50mL/min), the influence of adding HBr is small and the Si etchingquantity is substantially constant (approximately 100 μm), and theetching rate can be maintained. However, when the added flow rate of HBrexceeds 50 mL/min, the Si etching quantity is reduced as the added flowrate of HBr increases, and when the added flow rate of HBr exceeds 60mL/min, the etching rate is reduced by more than 20% (percentconcentration). In this state, the object of the present invention tosuppress the damage to the side walls of the Si trench while maintaininga constant etch rate cannot be achieved.

As for the Si trench etching quantity dependency representing the Sietching quantity (μm) with respect to the added flow rate of HBr,similar tendencies are shown when gases containing hydrogen other thanHBr, such as HI, HCl, H2, H2O and NH3, are used, and also when gaseshaving a gas containing hydrogen diluted by Ar, He or N2 as added gasare used, or when gases diluted in advance by the above-mentioned gasesare used. In the case of diluted gas, the quantity of gas containinghydrogen prior to dilution is considered as the added quantity.

The amount of HBr being added, or 60 mL/min, according to which thedamage to the side walls of the Si trench cannot be suppressed whilemaintaining the above-mentioned etch rate, corresponds to approximately16% (percent concentration) of the 380 mL/min of mixed gas composed of150 mL/min of SF6, 30 mL/min of O2 and 200 mL/min of SiF4.

FIG. 3(b) illustrates an Si trench side wall damage quantity dependency,which represents the amount of damage caused to the side walls of the Siwith respect to the added flow rate of HBr (mL/min).

When the added flow rate of HBr is small (about 0 mL/min), approximately140 nm of damage is caused to the Si side walls. However, the amount ofdamage is reduced by adding HBr, and when the added flow rate of HBrreaches 20 mL/min, the damage is reduced to approximately 15 nm, bywhich the amount of damage to the side walls of the Si trench is greatlyreduced compared to the case where no HBr is added. The added flow rateof HBr, which is 20 mL/min, corresponds to approximately 5% (percentconcentration) of the amount of mixed gas, which is 380 mL/min.

When the added flow rate of HBr is increased to exceed 5% (percentconcentration) and further gradually increased, the damage to the sidewalls of the Si trench is reduced, and substantially no damage is causedto the side walls of the Si trench for a while.

When the added flow rate of HBr is even further increased, the damage tothe sidewalls of the Si trench is gradually increased. When the addedflow rate of HBr is approximately 60 mL/min (approximately 16% (percentconcentration) of the mixed gas), a slight damage occurs to the sidewalls of the Si trench, but the level of the damage is practicallyacceptable.

When the added flow rate of HBr exceeds approximately 60 mL/min, aconsiderable amount of damage is caused to the side walls of the Sitrench, which becomes a problem. Further, when the added flow rate ofHBr reaches approximately 80 mL/min (21% (percent concentration) of themixed gas), a considerable amount of damage exceeding the acceptablelevel occurs to the side walls of the Si trench, by which the object ofsuppressing damage to the side walls of the Si trench while maintainingthe etch rate is no longer realized. This increase of damage to the sidewalls of the Si trench is considered to be caused by the radical speciescontributing to the etching (in this case, fluoride) becoming excessiveand reacting with the side walls of the Si trench, resulting in thedamage to the side walls.

The Si trench side wall damage dependency, which is the amount of damage(nm) caused to the side walls of the Si trench with respect to the addedflow rate of HBr, shows a similar tendency when gases containinghydrogen other than HBr, such as HI, HCl, H2, H2O or NH3, are used, andalso when gases having the listed gases containing hydrogen diluted withAr, He or N2 are used, or when gases being diluted by the aforementionedgases in advance are used. In the case of diluted gas, the quantity ofgas containing hydrogen prior to dilution is considered as the addedquantity.

FIG. 3(c) shows a selectivity dependency against mask, which is the maskselectivity with respect to the added flow rate of HBr. Here, maskselectivity refers to the ratio of the etching rates between thematerial to be etched (which is silicon in the present example) and thematerial of the mask (which is SiO2 in the present example). Regardingetching, it is important to carry out etching of the material to beetched without etching the mask material as much as possible. In anextreme case, if the mask selectivity is not good, the mask is removedeven before the target etch quantity of the material to be etched isachieved, and the etching cannot be completed. Therefore, it isnecessary to retain a high mask selectivity.

With reference to FIG. 3(c), the mask selectivity is gradually decreasedin correspondence to the added flow rate of HBr. With respect to themixed gas, the mask selectivity ratio is sufficiently high when theadded flow rate of HBr is within the range of approximately 5% (percentconcentration) to 16% (percent concentration).

As for the selectivity dependency against mask which is the maskselectivity with respect to the added flow rate of HBr, a similar resultis achieved when gases containing hydrogen other than HBr, such as HI,HCl, H2, H2O or NH3, are used, and also when gases having theabove-mentioned gases diluted with Ar, He or Ne are used, or when gasesbeing diluted with the above-mentioned gases in advance are used.

As described, it is recognized from FIG. 3 that when the added ratio ofHBr is 5% (percent concentration) or less, the effect of suppressingdamage to the side walls of the Si cannot be achieved. This isconsidered to be because there is not enough supply of depositingreaction products having side wall protecting effects. Moreover, if theadded amount of HBr is 16% (percent concentration) or greater, then thegeneration of reaction products having side wall protecting effectsbecomes excessive, deteriorating the etching carried out in the depthdirection. As a result, the etching ratio of Si is graduallydeteriorated, which is simultaneously accompanied by the deteriorationof the selectivity ratio against mask. Moreover, when the etching ratein the depth direction is deteriorated, the Br-based etchants alsobecome excessive and the side walls having been protected is subjectedto reaction again, and further damage to the side walls of the Si iscaused. From these results, it can be concluded that the ratio ofaddition of HBr should approximately be in the range of 5to 16% (percentconcentration).

FIG. 4 shows examples of the aforementioned etching profile. In astructure with a relatively small aspect ratio (the aspect ratio, whichis the ratio between the diameter of the trench opening 203 formed tothe substrate 202 to be processed and the depth, being about 5), asshown in FIG. 4(a), an etching profile having no damage caused to theside walls of the trench was achieved. Further, as shown in FIG. 4(b),also in a structure with a large aspect ratio (the aspect ratio, whichis the ratio between the diameter of the trench opening 203 formed tothe substrate 202 to be processed and the depth, being about 7), anetching profile having no damage caused to the sidewalls of the trenchwas achieved, and no problems such as etch stops occurred.

Further according to the plasma etching method of the present invention,the deposition probability of the generated deposition components can beimproved by reducing the electrode temperature in combination with theabove arrangement. This is considered to be the reason why in comparisonto the etching process performed in a temperature region equal to orabove normal temperature, the present method is capable of carrying outthe etching process without causing side wall damages, since theprotective layer is formed even under conditions where the amount ofreaction byproducts that form the protective layer to the side walls ofthe trench is small.

The processing conditions shown in Table 1 are typical etchingconditions used in the microwave plasma etching equipment with amagnetic field illustrated in FIG. 1. The processing conditions shownhere are adjusted for the present invention, and the optimum values ofthe process factors may somewhat vary in other etching equipments, suchas a helicon wave etching equipment, an inductively-coupled plasmaetching equipment, a capacitively-coupled plasma etching equipment, or amagnetic field RIE equipment. TABLE 1 Typical Etching Conditions of thePresent Invention Items Main Etch SF6 flow rate (ml/min) 150 O2 flowrate 30 SiF4 flow rate 200 Microwave (W) 800 Processing Pressure (Pa)4.0 RF bias (W) 20 Temperature of sample stage (deg. C.) −45 Coilcurrent (A) 14/14/4

The present method for suppressing the damage to the side walls intrench etching is not only applicable to the present equipment, but alsoapplicable to other etching equipments. Based on the processingconditions disclosed above, those familiar to the etching process caneasily adjust and optimize the conditions for other equipments.

1. An etching method for forming a trench (a groove or a hole) to asilicon substrate or a silicon substrate having a silicon oxidedielectric layer, the etching performed via a plasma generated by amixed gas formed by adding a gas containing hydrogen to a mixed gascomposed of SF6 and O2 or a mixed gas composed of SF6, O2 and SiF4,wherein the amount of added gas containing hydrogen is within a range of5 to 16% (percent concentration) of the total gas flow rate of saidmixed gas composed of SF6 and O2 or said mixed gas composed of SF6, O2and SiF4.
 2. The etching method according to claim 1, wherein said gascontaining hydrogen is HBr, HI, HCl, H2, H2O or NH3.
 3. The etchingmethod according to claim 1, wherein said gas containing hydrogen isHBr, HI, HCl, H2, H2O or NH3 being diluted by Ar, He or N2 when beingadded to the mixed gas, or said gas containing hydrogen is HBr, HI, HCl,H2, H2O or NH3 being diluted in advance by said gases.
 4. The etchingmethod according to claim 1, wherein said gas containing hydrogen doesnot contain carbon or fluorine.
 5. The etching method according to claim1, wherein a temperature of a sample stage for holding the siliconsubstrate or the silicon substrate having the silicon oxide dielectriclayer is controlled to 0 deg. C. or lower.
 6. An etching equipment forforming a trench (a groove or a hole) to a silicon substrate or asilicon substrate having a silicon oxide dielectric layer via a plasmagenerated by a mixed gas, the etching equipment comprising: a gasfeeding unit for feeding the mixed gas formed by adding a gas containinghydrogen to a mixed gas composed of SF6 and O2 or a mixed gas composedof SF6, O2 and SiF4, wherein the amount of added gas containing hydrogenis within a range of 5 to 16% (percent concentration) of the total gasflow rate of said mixed gas composed of SF6 and O2 or said mixed gascomposed of SF6, O2 and SiF4; and a sample stage for holding the siliconsubstrate or the silicon substrate having a silicon oxide dielectriclayer.
 7. The etching equipment according to claim 6, wherein said gascontaining hydrogen is HBr, HI, HCl, H2, H2O or NH3.
 8. The etchingequipment according to claim 6, wherein said gas containing hydrogen isHBr, HI, HCl, H2, H2O or NH3 being diluted by Ar, He or N2 when beingadded to the mixed gas, or said gas containing hydrogen is HBr, HI, HCl,H2, H2O or NH3 being diluted in advance by said gases.
 9. The etchingequipment according to claim 6, wherein said gas containing hydrogendoes not contain carbon or fluorine.
 10. The etching equipment accordingto claim 6, wherein a temperature of the sample stage for holding thesilicon substrate or the silicon substrate having the silicon oxidedielectric layer is controlled to 0 deg. C. or lower.